Who taught YOU to drive? A second look at headlights

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The latest headlamps actually produce less overall glare while providing more light on the road ahead, according to a University of Michigan research professor.

By Peter DeMarcoFebruary 26, 2012

Neither Irwin Rosenthal nor Michael Flannagan thinks that super-bright headlights necessarily make driving any safer. But that’s about all on which they agree.

For Rosenthal, an 82-year-old reader from Newton, high-intensity discharge lights, commonly called xenon headlights, are so bright that they nearly blind him while driving. “They should be banned,’’ he says.

But Flannagan, a headlight expert from the University of Michigan’s Transportation Research Institute, sees a different problem. He and his staff estimate that about 2,500 pedestrians are killed crossing roads at night each year, hit by drivers with headlights that aren’t bright enough to illuminate them.

“Glare is certainly a big problem for visual comfort in night driving. But the major safety problem is not glare, but rather a lack of light, even with the newer headlamps,’’ Flannagan says. “I know that really doesn’t fit people’s opinions and perceptions . . . but that’s what we’ve found.’’

A few weeks ago, I wrote about how much brighter headlights are today versus 20 years ago. The average halogen headlight is 40 to 70 percent brighter; high-intensity discharge lights can be more than 400 percent brighter; LED (short for light-emitting diode) lamps actually rival daylight.

The column triggered an e-mail deluge, with readers thanking me for corroborating their problems with headlight glare. The topic deserved further investigation, so for an alternative view I sought out Flannagan, a research associate professor who’s spent the past 23 years studying drivers’ vision.

What he had to say will probably flip whatever you think you know about headlights on its head.

Commercials for new headlights tend to emphasize their incredible brightness, like the catchy ad Audi ran during the Super Bowl that featured lamps powerful enough to vaporize vampires. But Flannagan says that brightness is really just half the story.

“The ads tell you how much light is given off in total by the lamp, but they don’t tell you how much light is hitting a certain point in the road,’’ he says. “The main thing is, is it shining light far enough down the road for you to see?’’

Surprisingly, that answer is almost always no, Flannagan says.

The National Highway Traffic Safety Administration has nearly 100 pages of rules that manufacturers must follow when designing car lights, making them one of the most intensely regulated parts of any car, Flannagan says. A number of those rules are aimed at reducing glare, including one very simple but significant requirement: To cut down on glare for oncoming drivers, a vehicle’s low-beam headlights must be pointed downward and to the right.

The requirement makes sense - imagine how glaring headlights would be without it - but it comes with a trade-off. Because your car’s headlights are angled to the right, you will have a harder time seeing pedestrians crossing from the left; because they are angled downward, you won’t be able to see more than a few hundred feet ahead.

Of the pedestrians killed at night, many are hit simply because drivers can’t see them soon enough to react in time, Flannagan says. Were headlights aimed farther down the road, many of those lives might be saved.

“Low-beam lamps don’t give drivers enough seeing distance to react to unexpected obstacles - mainly pedestrians - at speeds higher than 45 miles per hour at night,’’ he says. “But giving drivers the kind of seeing distances they really need to drive at 55 or 65 miles per hour at night is very tough without pushing up glare levels.’’

‘People actually underuse their high beams, which is a strange thing to say. People probably don’t recognize how limited their vision is with low-beam lights. And pedestrians shouldn’t assume drivers can see them.’

Michael Flannagan University of Michigan’s Transportation Research Institute

Your car comes equipped with lights that are aimed far down the road: the high-beam lamps. When headlights were first created, Flannagan says, the thinking was that the high beams would be your default lights, and you’d only temporarily switch to the low beams when another car was approaching or you were behind someone in traffic.

That’s not how drivers ended up using them. Most only rarely use their high beams, to avoid blinding oncoming drivers, and because it’s against the law to have them on when another car is approaching (in Massachusetts, it’s a $35 fine).

“People actually underuse their high beams, which is a strange thing to say,’’ Flannagan says. “People probably don’t recognize how limited their vision is with low-beam lights. And pedestrians shouldn’t assume drivers can see them.’’

Glaring problem

Given all the steps that manufacturers must take to reduce glare with low-beam lights, why do drivers, particularly older ones, still have problems?

“The bluish ones - they blind you,’’ Rosenthal says. “I was on a two-way road with a car coming the other way and I had to put my foot on the brake because I couldn’t see.’’

Flannagan agrees that glare is an issue for some drivers, but like other aspects of headlights, it’s often misunderstood.

New headlights, even the most powerful ones, actually produce less overall glare than conventional headlights, Flannagan says. They are better engineered, with more of the light they cast focused straight ahead. If we all drove on straight, flat roads, even the brightest headlights probably wouldn’t bother anyone.

But as we alluded to in our previous column on headlights, dips or sharp curves in the road can thrust an oncoming car’s headlights directly into your eyes. Under those circumstances, more powerful headlights are indeed more blinding, which is what drivers tend to remember.

People’s complaints about glare from truck headlights also are legitimate, Flannagan says, mainly because federal standards allow truck headlights to be mounted as high as 54 inches off the ground. At that height, they can indeed catch you at eye level.

Are bluish-tinged headlights also to blame for increased glare? Flannagan says he’s heard the complaint numerous times, but from a technical standpoint, bluish lights aren’t any more glaring than yellow or white ones.

“The color of headlamps doesn’t really matter much in terms of how well they help you see when you’re using them, or how much they hurt your ability to see when they’re a source of glare for you,’’ he says. “Generally people do find something more gentle on the eyes about a light that is less blue and more yellowish. But that’s a subjective perception, not an objective one.’’

Future solutions

So despite technological breakthroughs, we’re still driving with headlights that can be too glaring to oncoming drivers, while at the same time fail to light up enough of the road for safety purposes. Fortunately, in the not-so-distant future, all that could change, Flannagan says.

Research has begun on high-beam headlamps that will automatically narrow the light they project when another car is approaching, eliminating worries about glare for other drivers and making low-beam lights obsolete.

With LED lamps, manufacturers will be able to spin even more magic, creating headlights that narrow to reduce glare while simultaneously sending sideway beams of light to illuminate objects to the left of your car, such as a deer on the side of the road, or a pedestrian crossing the street.

“Ultimately, there is no technical obstacle to putting a digital projector on the front of a car that gives you what, a million pixels of light to work with?’’ says Flannagan. “With a projector like that, you can put light wherever you want it.’’

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